Consumer devices for recording and playback of recorded program material, such as movies, software and the like, are widely available. Media bearing such material include magnetic tape, recorded and played back using a VCR, and now more recently optical media such as CDs, CD-ROM's and DVD's. The DVD is new optical disk technology, capable of holding enough information typically for a 133 minute movie on each layer. The DVD often uses a so-called MPEG-2 data compression standard that enables video material to be efficiently stored and reproduced without significant visible degradation. Other standards for video and other types of information, such as embodied in software, can be utilized.
The cost of producing program material, such as entertainment movies, is considerable, whereas, the cost to the copyist is relatively low. Hence, movie piracy has become a substantial source of loss of revenue for the movie industry. Indeed, more than 2 billion dollars are lost to copyists annually, mainly in the form of bootleg video cassettes. DVD may make the situation even worse, as the audio and video programming from a DVD player have high fidelity and considerably more information content than that possible from VHS.
Two approaches to thwarting piracy have been implemented by legitimate producers of movies and other types of material having commercial value, such as software: (1) injecting, into a protected medium, a signal that distorts the material in some manner when played, and (2) watermarking, by injecting a visible or invisible static symbol or mark that identifies the source of the original material.
Watermarking commonly is performed on a medium at the point of authoring of protected material. An example is at a post house or other facility at which the information-bearing medium is produced. However, once recorded, the watermark is fixed. Although the watermark will identify the source of authoring of the material, it will provide no information on the identity of an unauthorized copyist. The identity of the copyist must be obtained from information gathered at the point of playback and copying. This may include such information as identification of the equipment used by the copyist and time of copying. Circuitry to provide this information at the playback unit, however, will increase the cost of the unit, a considerable disadvantage in this competitive industry. An objective of this invention is to produce a tracing signal at the point of use, that varies in dependence of, and is unique to, the copyist of a protected medium. Another objective is to do so without adding significant cost to the playback unit. An objective further is to carry this function out in digital or analog space, depending on the domain of the medium.
The protective signal furthermore must be unpredictable, as predictability will enable a copyist either to filter out the signal, or alter it so as to provide a false designation of source. The protective system further must be robust, as any source of copying message injected into the signal stream must be recovered in an environment having heavy transmission noise, and unintentional or intentional distortion. Furthermore, the sending message must be difficult to detect, modify or remove. The message content should be protected and difficult to decode, even if the transmitted bits identifying source are available. Finally, the output stream must be legal to enable proper decoding in the appropriate domain. An additional objective of this invention is to produce a point of use signal, injected into the signal stream of the protected medium, that is difficult for a copyist to detect or alter. The point of use signal furthermore should be able to be injected into any type of protected content, including audio and software, in addition to video.